L5 - Hydropower

Question 1

What is hydro energy

Answer 1

• Hydro energy is like other renewables which are indirect solar power
• Energy becomes available when rain/snow falls on high land
• The natural route back to sea for rain and snow on high land is streams and rivers

Question 2

Power supplied

Answer 2

• Supplied at the rate at which energy is delivered

P = 1000 (density of water) * Q * g * H * n

Q = velocity (m3/s)
H = effective head taking into account energy losses
Actual head is the difference in elevation between the water levels upstream and downstream
n = turbo generator efficiency. hydroelectric turbo generators are one of the most efficienct machines, losses at a few % of input power

Question 3

Resource capture/conversion technologies

Answer 3

• Water wheels

Question 4

Installation type

Answer 4

• Low head: river flow
• Medium head: reservoir
• High head: high reservoir

Question 5

Modern turbine types

Answer 5

• Francis
• Fixed pitch propeller - used for lower heads and large volume flows
• Turgo
• Pelton - used for high head
• Kaplan
• Crossflow

Question 6

Purpose of storage for hydropower

Answer 6

• To make water available when required to meet the electrical system load
• Provision of storage means that the water may be utilised during seasonal variations and annual variations.
• Increase in storage eases operation but cost of storage can be high

Question 7

Methods of storage

Answer 7

• Embankment dams
• Solid gravity dams
• Buttress dams

Question 8

Economics of hydro power stations

Answer 8

• Cost per kWh of energy generated is higher than conventional power stations
• This is due to high capital costs of extensive civil engineering works and long periods of construction

However, operating costs are very low:

• no fuel costs
• additional fixed costs of running the plan are comparable with themal power stations
• Cost of borrowing is one of major factors influencing viability.
• often projects can be implemented only by using larger schemes eg irrigation, flood control, navigation

Question 9

Environmental impacts of hydroschemes

Answer 9

• Emit very little CO2 once in operation
• Storage schemes have a higher footprint than run of river schemes as they require large amounts of raw material
• Run of river schemes have ery small reservoirs or none at all. Carbon footprints for this are some of the lowest of all electricity generation tech
• Sedimentation from weather rock etc are trapped in the reservoir.
• Hydropower projects have impacted fish and fisheries by changing habitat quality and availability, changing flow regime and fish passage
• Changes in water quality are often experienced both upstream and downstream of a dam. This includes increased/decreased dissolved oxygen, increase in total dissolved gas, modified nutrient levels, thermal modification and heavy metal levels

Question 10

Wave hydropower

Answer 10

• Wave energy is a form of concentrated solar energy.

- Part of the energy of winds which blow over large areas of water is converted into wave energy

Question 11

Tidal energy

Answer 11

• Reliable and plentiful but converting it into useful electrical power is not easy

Question 12

Summary

Answer 12

• Efficiency of water based turbines is high

- Capital costs is has